7.2.1 Selectable Data

The concept of selectable data requires some explanation. This is used to indicate the data variables you might ordinarily use to narrow your search for data in the first pass at a dataset.

For geophysical data, the selectable data is often the time and location of the data, since typical searches for data often begin by specifying a part of the globe that bears examining, or a date of some event. For other types of data, other data variables will seem more appropriate. Model data, for example, which has no real location or time, might be arranged by the parameters that varied between runs.

A comprehensive definition of selectable data has so far eluded the OPeNDAP group, but there are some guidelines, albeit fairly vague ones:

• The selectable data is generally not recorded within each data file. However, the selectable data may often include a range summarizing some of the data within each file.
• The selectable data should help a user decide whether a particular data file in a dataset is useful. A temperature range might not be as useful as a time range, since data searches more often start with time. (Both would presumably be still more useful, but there is a trade-off between the utility of the file server and the time spent maintaining it.)